Solvent extraction of lubricating oils



Dec. 26, 1939. A. SCHLAGETER 2,134,961

SOLVENT EXTRACTION OF LUBRICATING OILS Filed Sept. 1, 1936 :wrzner om Y I 14 TREATR YFLI P11. 0 5

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Patented Dec. 26, 1939 PATENT, OFFICE SOLVENT EXTRACTIIOlgI OF LUBRIOATING August Schlageter, N. D. de Gravenchon, Seine Inferieure, France,

assignor to Standard Franco-Americaine de Baffinage, a. corporation of France Application September 1, 1936, Serial No. 98,863

4 Claims.

This invention relates to the solvent extraction of lubricating oils, and is more particularly concerned with certain improvements in the process when carried out in a continuous counter-current manner.

It is already known that many solvents such as phenol, cresylic acid, liquid sulfur dioxide, nitrobenzene, chlorex, furfural, etc. are capable at suitable temperatures and in suitable quantitles of separating lubricating oils into their respectively more paraffinic and saturated and more aromatic and unsaturated hydrocarbon constituents. Various methods have been proposed for this purpose, and it has been found that a continuous counter-current method is especially satisfactory.

In the continuous counter-current method of treating, lubricating oil is introduced at one end of the system and solvent at the other. The system may consist of a single, tall tower, or of a series of separate but inter-connected stages.

The solvent has preferentia1 solvent power for the aromatic and unsaturated portions of the oil and these are dissolved in the extract phase. The parafilnic and more saturated portions of the oil do not dissolve to any extent in the solvent and are removed as a rafilnate phase.

It happens, however, that some of the paraffinic or good oil does dissolve in the solvent and is removed in the extract phase,

Various methods have been proposed for recovering this so-called cycle oil from the extract, and recycling it through the treating proc- One such method is to cool the extract phase, whereupon the solubility of the oil in the solvent is decreased, and some of the oil is therefore thrown out as a separate phase which may be readily removed from the solvent.

The present invention is directed to certain improvements in this cooling method of cycle oil recovery. The improvement consists essentially in cooling the extract in stages and returning cycle oil recovered in each stage to different stages of the treating process.

The difierent cycle oils are preferably introduced at temperatures corersponding to those in the treaters into which they are injected.

The improved method will be fully understood from the following description read with reference to the accompanying drawing, which is a semi-diagrammatic view in sectional elevation of a suitable type of apparatus for carrying out the process.

Referirngto the drawing, numerals I, 2, 3,

4, 5, 6 and 1 designate the stages of a seven-stage counter-current treater. Numeral 8 designates a supply tank for the oil to be treated.

Lubricating oil is withdrawn from tank 8 through line Ill, passed through heater H, wherein the temperature is raised to the required treating temperature, and thence passed through lines 12 and I3 into the first treater I. Mixing devices, such as orifice mixers, are provided in the lines entering each treater. These are designated by letters a, b, c, d, e, f, and g.

Solvent is withdrawn from tank 9 through line i l, passed through heater or cooler l 5 and thence passed through line l6 and mixer g and introduced into the last treater 'l.

Rafiinate from treater l is removed through line H and introduced through mixer b and line l8 into the second treater 2. Raffinate from treater 2 is removed through line l9, passed through mixer c and introduced through line 28 in the third treater 3. Rafiinate from treater 3 is withdrawn through line 2|, passed through mixer d and line 22 and introduced into treater l. Raffinate from treater 4 is withdrawn through line 23, passed through mixer e and line 24 and introduced into treater 5. Rafiinate from treater 5 is withdrawn through line 25, passed through mixer and line 26 and introduced into treater ii. Raifinate from treater 6 is withdrawn through line 21, passed through mixer g and line I6 and introduced with fresh entering solvent into treater l.

In a similar manner extract from the last treater l is removed through line 28 and introduced through mixer f and line 26 into the sixth treater 6, and extract from each treater is introduced into the next preceding treater.

Final extract from treater I is removed through line 29 and passed into the first of three or more cooling stages designated C1, C2 and C3. In the first cooler C1 temperature is partially reduced whereby another separation of phases occurs. The cycle oil phase is removed from cooler C1 through line 36 and introduced into the third treater 3 through mixer c and line 20. The solvent phase from C1 is removed through line 3! and introduced into C2 where temperature is further lowered causing another separation of phases. The cycle oil phase from C2 is removed through line 32 and introduced into treater 2 through mixer b and line I8. 31 is a heater.

The solvent phase is removed from C2 through line 33 and introduced into 03 where the temperature is lowered still further and another separation of phases occurs. The cycle oil phase from C3 is removed through line 34 and introduced into treater I through mixer a and line I3.

The solvent phase from C3 if this is the last 0001- ing stage, is withdrawn through line 35 and collected in spent solvent tank 36.

It will be understood that more or less than seven treating stages may be used. and that more than three cooling stages may be used. Alternatively the treating may be carried out in a single counter-current tower and the cycle oil from each cooling stage may be introduced into the finate, the composition (paraffinicity) of which is similar to the composition of the cycle oil. Introducing the cycle oil into its appropriate treater brings about the least disturbance to the equlibrium of the phases in presence. The possibility of overloading a treater by introducing a cycle oil of a widely different composition, as is very often the case when returning the cycle oil obtained in one-step cooling to any one treater, is greatly reduced.

.The better equilibrium obtained between the phases in the treaters when injecting the cycle oils produced by the improved cooling method as compared to the injection of a cycle oil obtained by one-stepcooling will permit:

(a) Decreasing the per cent of phenol used for the V. I. improvement on the oil,

(b) Increasing the thruput on account of the lower per cent of phenol used for the same V. I. improvement,

(c) A higher treating temperature. The settling time will be reduced in the treater because the viscosity of the phases is lowered. This will allow a further increase of the thruput.

To maintain a high temperature in the treaters for a given V. I. improvement on the oil a large quantity of cycle oil should be produced in the coolers. The total cycle oil injected in one treater will overload it whereas the same quantity of cycle oil produced by the-fractionating method and injection in the respective treaters will considerably reduce the magnitude of this trouble. Less entrainments. will take place for the same thruput because the phases in the treaters will be more stable, and the yield of raflinate for the same V. I. improvement will be 1 higher for the some reason.

This invention is not limited to any particular solvent, nor is it limited by any of the de-.

tails which have been given merely for purposes of illustration but is limited only in and by the following claims in which it is intended to claim all novelty inherent in the invention.

I claim: 1. In the counter-current solvent treating of lubricating oils, the improvement which comprises cooling the extract phase in a series of cooling stages, removing the cycle oil phase from each cooling stage and returning the first obtained cycle oil to a point approximating the middle of the treating zone and the last obtained cycle oil to a point of the treating zone nearer the extraction end before the first cooling stage, intermediate cycle oils being returned to' the mineral oil into a rafiinate and an extract of different solubility in the solvent, the steps which comprise subjecting the solvent containing the extract to a plurality of cooling stages, withdrawing the oil phases separated from the solvent in each of these stages and returning such oil phases to the extraction process at diife'rent points, the first oil phase produced by the cooling being returned at a point nearer the ratfinate end and the oil phases produced by successive cooling steps at points successively further from the raflinate end, said oil phases all being returned at points between the rafiinate end and the first cooling stage.

3. Process according to Claim '2 in which the oils produced by cooling ofthev extract are re-- turned'to the treating process at pointsselectecl so that the returned oil will mingle with oil of substantially the same parafiinicity. T

4. Improved process of solvent treating mineral oil comprising treating said oil with a selective solvent under conditions to form a solvent extract phase and a raffinate phase, separating the solvent extract phase from the raminate phase and subjecting the solvent extract phase to a plurality of cooling stages, withdrawing the oil phases separated from the solvent extract phase in each of these cooling stages and returning the respective oil phases to the extraction process at different points, the first oil phase produced by the cooling being returned at a point ing returned to points successively further from the rafiinate end respectively, said oil, phas'esall being returned at points between the raflinate end and the first cooling stage.

AG. SC'I-ILAGETER. 

